1. Field of the Invention
This invention relates to an improved mechanical interrelation of the components of an electrical medical lead system for allowing the reversal of the electrical interconnection of inner and outer coaxial coiled wire conductors with other components of the lead system, and particularly, for the use of such an adaptor in a pacing lead system having a physiologic sensor incorporated therein.
2. Brief Description of the Prior Art
Electrical medical lead systems of many types are known in the art and commonly comprise a proximal connector portion having one or more connector elements, an elongated insulated lead body having one or more mutually insulated electrical conductors extending therethrough and one or more mutually insulated electrodes arranged at or near the distal portion of the lead system. Electrical medical lead systems may be employed in pacing, neurologic stimulation, cardioversion/defibrillation and in numerous other applications where such lead systems are introduced temporarily or implanted permanently within the patient's body to provide an electrical interconnection between a site where electrical stimulation is to be delivered or electrical signals of the body are to be detected and a more remotely situated stimulator or sensing apparatus.
In such lead systems, coiled wire conductors have been employed for many years, originally in side by-side relation and more recently in coaxial relation to one another. Also more recently, it has become common to incorporate physiologic sensors, such as blood pressure sensors, oxygen sensors, temperature sensors, or the like, within the lead body for providing physiologic monitoring of the selected parameter in conjunction with the sensing of electrical events and the delivery of electrical stimulation. In the pacing context, for example, numerous sensors have been incorporated in lead bodies, including those enumerated in the article entitled "Principles of Exercise Responsive Pacemakers," IEEE Engineering in Medicine and Biology, June 1984, pp. 25-29, by Fearnot, N.E. et al. Further sensors are enumerated in the article entitled "Research Leads to Major Breakthrough in Rate Responsive Pacemaking," by Kenneth M. Anderson on pp. 89-93 of Medical Electronics of October 1986.
Such sensing systems for both pacing and cardioversion systems include pressure sensors incorporated into housings positioned along the lead body as disclosed in U.S. Pat. Nos. 4,407,296 to Anderson, and 4,485,813 to Anderson et al, incorporated herein by reference in their entireties. Considerable activity has also been expended in the incorporation of oxygen sensors in pacing and cardioversion leads, as shown, for example, in U.S. Pat. No. 4,815,469 to Cohen, et al, and patents referenced therein.
A number of design constraints are placed on the characteristics of the materials used in and the physical size of components of modern pacing and cardioversion leads. Incorporation of physiologic sensors into these lead systems adds complexity and increases reliability issues concerning the size, performance, and longevity of the lead system. The above-referenced '296, '813 and '469 patents attempt to address the manner in which the electrical interconnections are effected in a pacing lead in the presence of a relatively bulky pressure or oxygen sensor. It is desirable to accommodate pacing or cardioversion and sensing functions employing the minimum number of electrical conductors and associated connector elements while maintaining operational flexibility in the use of the elements of the system, high reliability, and over all lead flexibility and handling characteristics desired by the physician users.
With these considerations in mind, the '813 patent addresses the reduction of the number of lead conductors and associated connector elements to allow for connecting at least one pace/sense distal electrode and the distally located pressure sensor to a pacing pulse generator. The pressure sensor disclosed therein is cylindrical in shape and its outer conductive housing constitutes one of the electrical signal return paths of the sensor transducer located therein by a conductor connected thereto. The active circuit components of the pressure sensor are connected by a feed-through extending axially from one end of the housing to a separate conductor.
Although not specifically described in the '813 patent, leads constructed in accordance with its teachings and implanted in clinical testing were constructed with co-axial inner and outer coiled wire conductors. The inner and outer coiled wire conductors were connected distally to the feed-through and cylindrical housing, respectively, of the pressure sensor and proximally either to proximal pin and ring shaped, in-line connector elements, respectively, or to bifurcated connector pins. The distal tip pace/sense electrode was connected by a short conductor coil to the cylindrical housing of the pressure sensor, and both were insulated from the body environment. Thus the tip electrode was connected to the ring shaped, in line connector element or one of the bifurcated connector pins.
The '469 patent addresses a number of approaches to the interconnection of the pace/sense electrodes with the active components and housing of an oxygen sensor within a pacing lead body. The lead system depicted therein employs side-by-side coiled wire conductors for providing an electrical connection between the active components of the sensor and the pacing electrodes, where the coiled wire conductors pass through apertures within the sensor housing or are electrically connected to the sensor housing in order to interconnect the active sensor components and the pace/sense electrodes with appropriate connector elements at the proximal end of the lead. Although one embodiment depicts the employment of a pair of coaxially oriented coiled wire conductors, they extend through the sensor housing to interconnect distal tip and ring pace/sense electrodes with proximal connector elements. A separate, parallel oriented, coiled wire conductor is interconnected with the feed-through of the active components of the sensor and a proximal connector element.
It is generally undesirable to employ coiled wire conductors extending the length of the lead body in parallel or side-by-side relation in view of problems that may arise in the unequal flexing forces applied to the side-by-side coiled wire conductors when the lead is implanted. In a multi-filar, coiled wire conductor lead system employing modern conductor diameters, it is preferred to employ a coaxial arrangement as described above. However, the use of the coaxial conductors extending from the proximal connector elements of an in-line connector to the distal components of the lead normally requires that the inner conductor be electrically connected to the proximal most connector element or pin and the outer conductor or conductors be connected to the more distally located connector elements. Since the lead body is desirably cylindrical throughout its length and the sensor housings are likewise cylindrical, the outer conductor is normally connected to the sensor housing and the inner conductor is connected to the active elements of the sensor through its feed-through, which extends axially with respect to the lead body all as described above.
In order to allow replacement of pacing pulse generators with pacing leads already implanted in a patient, each manufacturer initially developed its own size and spacing convention for its pulse generator connector elements and leads, connector pins, rings and insulators. Subsequently, an industry-wide standard was proposed for specifying the size and location of connector elements on lead bodies and within the connector blocks of in-line connector pacing pulse generators to allow interchangeability of pacing lead and pulse generator products within the industry. A precursor to this standard was set forth in the article entitled "A Voluntary Standard For 3.2 mm Unipolar and Bipolar Pacemaker Leads and Connectors," by Calfee, et al, PACE, Vol. 9, pp. 1181-1185, 1986, incorporated herein by reference in its entirety. The current draft standard (ISL DIS 5841 3.3) is popularly referred to as the "IS-1" Connector Standard. Lead connectors conforming to the IS-1 Connector Standard are disclosed in U.S. Pat. Nos. 4,951,687 and 5,007,435, incorporated herein by reference in their entireties.
The IS-1 standard dictates that the proximal-most connector pin of the in-line connector be coupled electrically with the distal-most pace/sense electrode of a pacing lead system. Since the proximal pin connector element is coupled to the inner coaxial coiled conductor, the bulk of the sensor body obstructs the connection of the inner coil conductor to the distal tip electrode.